1. Field of the Invention
The present invention relates to a luminescent device and a method for manufacturing the same, and more particularly to a luminescent device composed of a light emitting diode having high heat radiation and a method for manufacturing the same.
2. Description of the Background
In a conventional luminescent device, a pair of leads is combined by the transparent resin which was shaped by molding. At an end of an inner lead of a first lead, a light emitting diode is mounted, and an electrode of the light emitting diode and an end of an inner lead of a second lead are connected by a metal wire.
Outer leads of the first and second leads are bent in a gull wing shape or a J shape. The ends of the outer leads are soldered to the substrate. The portion where the light emitting diode is mounted is sealed with the transparent resin on the overall periphery, so that the heat from the light emitting diode is mainly transmitted to the lead, and is radiated to the substrate.
Each lead is separated and formed from a lead frame. As a material of the lead frame, an article that is the copper, which is a material having high thermal conductivity and electric conductivity, coated with a plating film for oxidation prevention is widely used.
A luminescent device is expected as a new-generation light source following an incandescent lamp and a fluorescent lamp, and is required for the higher luminance. As one of the means for realizing the high luminance, supplying a large current to a light emitting diode may be cited.
However, the efficiency of the present light emitting diode is said to be 10 to 20%, and the remaining 80 to 90% of the electric energy is converted to heat. As the operation temperature rises, the efficiency of the light emitting diode lowers, and when the operation temperature becomes higher than 130° C., the deterioration of the light emitting diode itself proceeds.
Therefore, to operate the light emitting diode by a large current, it is necessary to improve the heat radiation from the light emitting diode. Products having a constitution designed so as to enhance the heat radiation are manufactured by various companies for manufacturing luminescent devices.
In such products, the sectional area is increased by changing the width and the thickness of the lead, and thus the heat capacity and heat resistance of the leads are improved, or each inner lead is made contact with a heat sink composed of a copper block and is formed integrally with it, and thus the diffusion of heat is promoted.
However, when additional parts are introduced like these, the number of the parts of the luminescent device is increased, the constitution thereof is complicated, and thus the productivity therefor gets worse. Further, the parts of the luminescent device are made larger, and thus the problems arise that an increase in the part weight results and the size of each part itself does not correspond to its use.
For example, when intending to build in a flash in a mobile phone having a built-in image pickup device, it is necessary for the flash source to emit light as bright as possible and to be as small and light as possible. But it is difficult to provide a bright light source suited to such a use.